The US drug safety system developed fitfully through a series of historical accretions, typically in the wake of major drug safety scandals. In 1962, largely precipitated by the thalidomide tragedy, the Kefauver-Harris amendments to the Federal Food, Drug, and Cosmetic Act required the sponsor to provide “substantial evidence” of both safety and efficacy during a premarket evaluation. The resulting multistage approval process improved the evidence base for premarket regulatory decision making about drugs, but it also created, as an unintended consequence, a postapproval environment in which sponsors were largely free from requirements for additional evaluations. At approval, the sponsor's scientific teams responsible for meeting US Food and Drug Administration (FDA) requirements were generally replaced by marketing teams, and the manufacturer's efforts, energies, and studies were generally directed toward marketing its drugs.1,2